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SEI Strategy

Our primary strategy is to approach testing using a fault centered test development but without abandoning the functions that the UUT needs to perform at the next level of assembly.

Due to the complexity of design, the fault universe of newer UUT' expanded to the point that tracking of each fault became time, and therefore cost prohibitive. The industry moved towards functional testing. This was natural since UUT designers think in terms of performance and functions and thereby could easier develop tests for functions. The limitations of function-based thinking can be illustrated in a recent project. We found that an LCD in an avionics LRU was tested but there were parts left over. The LCD could be tested to see if it functioned properly but upon closer scrutiny of the possible faults

we found a heater and related circuitry that assisted the LCD to function at lower temperatures. The primary function was tested but a set of faults we missed that could cause potential malfunction and degraded operation. Our example is trivial in view of the multi-function chip technology we face today, where many important, hidden, functions could be missed.

Working from functions to tests can leave a significant number of faults of the UUT fault universe undetected even though all the known functions were exhausted.